In the continuous flow method of pasteurizing milk, etc., it is subjected to a high temperature, usually above 161 degrees F., in order to destroy certain microorganisms and prevent or arrest fermentation. For efficient utilization of the heat energy required, the heated, pasteurized product and the relatively cold, raw product are passed through a heat exchanger. This is sometimes called a regenerator. This cools the pasteurized product while preheating the raw product by heat transfer across stainless steel plates.
It is absolutely essential, and the public health laws and regulations reflect this, that the pasteurized product in the heat exchanger be at a higher pressure, typically about four psi, than raw product, to prevent contamination. For this purpose, a differential pressure indicator and control unit is required for each milk pasteurizer to show the pressures of the respective pasteurized and raw products in the heat exchanger. Further, the unit is commonly provided with a differential pressure switch which de-energizes the pump or pumps of the pasteurization system and renders it inoperable if the required pressure differential is not maintained.
One of the important responsibilities of the milk plant inspector is to check the differential pressure indicator and control unit and verify that it provides accurate pressure readings and will in fact automatically close down the system if the minimum pressure differential is not maintained across the plates of the heat exchanger.
There is a need for a simple and dependable apparatus to test dual pressure indicator and control units of this kind.